The present invention relates to the hydrocracking of coal and other carbonaceous material. The materials contemplated include anthracite, bituminous and lignite coal, as well as peat, oil shale, tar sand, wood, lignin, solid petroleum residuals and other related materials. However, the development is particularly applicable to the conversion of lignite and bituminous coal to liquid and gaseous products.
The hydrocracking or hydropyrolysis of coal is the thermocracking of coal in the presence of hydrogen. Reaction temperatures and pressures are moderately high from 1400.degree. to 1800.degree. F. and from 1500 to 2500 psig. When solid coal particles are heated the volatile matter is released. The initial devolatilization appears to take place in two broad steps. In the first step moisture, carbon oxides, chemically formed water, tars and methane are released from a reactive semi-char. Upon further heating, semi-char is dehydrogenated to a less reactive char. The large flow of gases from the particles in the initial stages prevents hydrogen from entering the coal particles and diffusing to react with coal hydrocarbons. The materials emitted during coal pyrolysis diffuse into the bulk gas phase where reactions such as tar hydrogenation can take place.
Coal hydropyrolysis results in a pluralilty of hydrocarbon products including both aliphatic and aromatic compounds. Various products including alkanes as well as aromatics such as benzene, ethylbenzene, indenes, toluene, xylenes, phenols, napthalenes, and cresols may be included. It is important that the relative amounts of these various materials be controlled in a manner to accommodate the desired products. High octane materials for gasoline blending or feed stocks for chemical processing may make various product distributions desirable.
It has been found that process variables in the hydropyrolysis process can be altered to change product distributions. Changes in pressures, final reaction temperatures and high temperature histories are effective to produce variations in the relative amounts of the hydropyrolysis products. One method involving changes in the temperature profile is disclosed in the assignees co-pending application by Duncan, Ser. No. 15,258, filed Feb. 26, 1979, entitled "Process for Hydrocracking Carbonaceous Material to Provide Fuels or Chemical Feed Stock".